Nigerian soldiers were hounded out of their Baga base by suspected Boko Haram militants on Saturday.
The militants seized have seized the base after a series of blistering raids near Lake Chad, sending soldiers and civilians fleeing, witnesses said on Sunday.
According to residents, the gunmen killed several people, burnt hundreds of homes and looted scores of businesses in Saturday’s attacks, although there was no official death toll.
Baga, scene of a Nigerian army massacre in 2013, was the last town in the Borno North area under government control.
It hosted the base of the Multi-National Joint Task Force (MNJTF), made up of troops from Nigeria, Chad and Niger.
Set up in 1998 to fight trans-border crime in the Lake Chad region, the force more recently took on Boko Haram.
Boko Haram attacks towns and villages on an almost daily basis, abducting people including young boys and girls, BBC Africa analyst Mary Harper reports.
The military, which includes Western advisers and surveillance, seems incapable of dealing with the problem, she adds.
Residents who fled to Chad said they had woken to heavy gunfire as militants stormed Baga early on Saturday, attacking from all directions.
They said they had decided to flee when they saw the multi-national troops running away.
Maina Maaji Lawan, senator for Borno North, told BBC World Service civilians had run “helter skelter” – “some into the forest, some into the desert”.
Communications with the town were cut off and exact information about casualty numbers could not be confirmed, he said.
“We are very dispirited,” the senator added.
Confirming that the military had abandoned the base, he said people’s frustration knew “no bounds” over the apparent fact that the military had not fought back.
“There is definitely something wrong that makes our military abandon their posts each time there is an attack from Boko Haram,” the senator said.
Residents of Kauyen Kuros, Mile 3, Mile 4, Baga, Doron-Baga and Bundaram fled across the lake in fishing boats and canoes into Chad following the hours-long attacks by hundreds of militants from the Islamist group.
“We are now seeking refuge in Gubuwa, Kangallam and Kaiga villages inside Chad near the border with Nigeria,” Dansubdu told AFP by telephone from Gubuwa.
The gunmen killed several people, burnt hundreds of homes and looted scores of businesses in the attacks that lasted over seven hours, said Doron-Baga resident Lawan Ajikalumbu who also fled to Gubuwa.
There was no official casualty toll.
Abubakar Gamandi, head of the fishermen’s union in Borno state and a resident of Baga, said he received several calls from union members who fled to neighboring Chad informing him of the attacks.
Baga was the scene of the deadliest Boko Haram attack in April 2013 when 185 people were killed and more than 2,000 homes were destroyed in fighting between the Islamists and members of the multinational force.
Suspected Boko Haram gunmen late Saturday also raided the town of Babban Gida, 50 kilometers (30 miles) from Damaturu, the capital of neighboring Yobe state, according to residents.
The militants destroyed the military barracks, torched a deserted government boarding school and a local administration building after overpowering soldiers in a gunfight, they said.
